Tappet for the valve gear mechanism of an internal combustion engine

ABSTRACT

A tappet (1) comprises an annular section (2) which concentrically surrounds a circular section (5). The two sections (2, 5) can be loaded by cams (4, 7) of different lift and be coupled to each other when desired by radially displaceable sliders (11, 14). To avoid switching errors, the slider (11) extending in the annular section (2) can be selectively prevented from being displaced by a piston (26) which comprises a control edge (28) and is displaceable in the longitudinal direction of the tappet (1). For this purpose, the piston (26) cooperates with a groove (29) of a cam (4) starting from a second part (β) of the base circle of the cam. During this part (β) of the base circle, the piston (26) can be displaced by hydraulic medium pressure in cam direction into the groove (29) so that it extends with its control edge (28) in an annular groove (30 or 31) of the first slider (11) and thus locks this slider (11) out of its desired displacement phases.

This application is a 371 of PCT/EP97/03089 filed Jun. 13, 1997.

DESCRIPTION

1. Field of the Invention

The invention concerns a tappet for a valve train of an internalcombustion engine, said tappet being designed to be switched todifferent valve lifts including a tappet (1) for a valve train of aninternal combustion engine, which tappet (1) can be switched todifferent valve lifts and is comprised of an outer annular section (2)which concentrically surrounds a circular section (5) which is axiallydisplaceable relative thereto, both sections (2,5) being loadable inlift direction in the regions of their bottoms (3,6) by cams ofdifferent lifts, or at least one section being loadable by at least onecam in the lift direction, each of the sections (2,5) comprising in theregion of its bottom (3,6) at least one reception (9,10) extendingradially said receptions (9,10) being aligned to each other in a cambase circle phase, there being arranged in the reception (9) of theannular section (2) a first slider (11) which is displaceable by a servomeans towards the reception (10) of the circular section (5), and saidfirst slider (11), for realizing un uncoupling of the sections (2,5)extends with an inner end face (12) up to a position immediately infront of an annular surface (13) between the sections (2,5), and, forrealizing a coupling of the sections (2,5), acts on a second slider (14)which extends through an entire length of the reception (10) of thecircular section (5), so that both sliders (11,14) overlap the annularsurface (13) by their peripheral surfaces (20,21) to establish a coupledstate.

2. Background of the Invention

A tappet of the pre-cited type is known from DE-OS 43 14 619 and doesnot need to be described more closely here. A drawback of this tappet isthat it comprises no means to exclude switching errors of its pistonswhich function as coupling means. The pressure-medium loaded pistonsreceive no information as to when it is technically appropriate tooverlap the annular surface between the two parts of the tappet. Sincesuch a tappet is switched, as a rule, in the base circle phase of thecam in which its two sections are aligned to each other in the region oftheir bottoms, it is possible, for example, at high engine rotationspeeds, or due to other influences such as pressure medium fluctuationsand the like that, when leaving the base circle of the cam, i.e. at thestart of the run-on flank, the coupling means have not yet reached theirposition of coupling or uncoupling as the case may be. If, in thistransition state, the coupling means concerned overlaps the annularsurface between the two sections only slightly, cam lift on the outersection can break off leading to a destruction of components or to anextreme noise generation.

OBJECT OF THE INVENTION

It is therefore the object of the invention to create a tappet of thepre-cited type in which the mentioned drawbacks are eliminated and, moreparticularly, using simple means, to create a mechanism which excludesswitching errors in the aforementioned operating states, that is to say,a mechanism which enables an axial displaceability of the coupling meansonly in the base circle phase.

SUMMARY OF THE INVENTION

The invention comprising a tappet (1) for a valve train of an internalcombustion engine, which tappet (1) can be switched to different valvelifts and is comprised of an outer annular section (2) whichconcentrically surrounds a circular section (5) which is axiallydisplaceable relative thereto, both sections (2,5) being loadable inlift direction in the regions of their bottoms (3,6) by cams ofdifferent lifts, or at least one section being loadable by at least onecam in the lift direction, each of the sections (2,5) comprising in theregion of its bottom (3,6) at least one reception (9,10) extendingradially said receptions (9,10) being aligned to each other in a cambase circle phase, there being arranged in the reception (9) of theannular section (2) a first slider (11) which is displaceable by a servomeans towards the reception (10) of the circular section (5), and saidfirst slider (11), for realizing un uncoupling of the sections (2,5)extends with an inner end face (12) up to a position immediately infront of an annular surface (13) between the sections (2,5), and, forrealizing a coupling of the sections (2,5), acts on a second slider (14)which extends through an entire length of the reception (10) of thecircular section (5), so that both sliders (11,14) overlap the annularSurface (13) by their peripheral surfaces (20,21) to establish a coupledstate, characterized in that

one of the sliders (11 or 14) whose section (2 or 5) cooperates with acam (4 or 7) is surrounded on its peripheral surface (20 or 21) at leastpartially by a recess (25) of a piston (26) or a piston-like element,

the piston (26) or the piston-like element is displaceable in an axialdirection of the tapped (1) by a servo means, and the recess (25)comprises a cam-remote control edge (28) which engages the slider (11 or14),

the piston (26) or the piston-like element extends through an aperture(27) of the bottom concerned (3 or 6) and cooperates with a groove (29)extending in a peripheral direction on the outer peripheral surface (38)of the associated cam (4 or 7), said groove (29) starts on a second part(β) of the base circle,

one of the sliders (11 or 14) comprises two annular grooves (30,31) intowhich the control edge (28) of the piston (26) or the piston-likeelement can be selectively displaced when said piston (26) orpiston-like element is simultaneously engaged in the groove (29) of theassociated cam (4 or 7), and

the annular grooves (30,31) are spaced from each other so that when thecontrol edge (28) displaced into the radially inner annular groove (30),the sliders (11, 14) extend entirely within their respective receptions(9,10) for uncoupling the sections (2,5) and when the control edge (28)is displaced into the radially outer annular groove (31), the peripheralsurfaces (20,21) of the sliders (11,14) overlap the annular surface (13)between the sections (2,5) for coupling the sections (2,5).

The measures of the invention provide a simple technical means fordelivering information to the tappet as to when it is in communicationwith the base circle of the cam. In this way, the initially mentionedswitching errors are substantially excluded, and coupling and uncouplingby the piston which cooperates with the annular grooves of the sliderare permitted only during a first part of the base circle of theassociated cam.

The entire device is configured so that the piston, or another similarlysuitable element, is displaced into the groove of the cam when thesliders have to be locked in place. It is proposed to load the piston inits locking direction by a servo means such as a hydraulic medium.However, it is also conceivable to spring load the piston in the lockingdirection by a compression spring or by a combination of hydraulicmedium pressure and the force of a compression spring. The pressingforce of the piston is adjustable through its cross-section and throughthe hydraulic medium pressure. It is also conceivable to use othermechanisms for this purpose, such as magnetic, electromagnetic or purelymechanical means and the like. Further, the piston may have a geometricshape quite different from the one shown in the drawing, the onlyimportant thing being that the sliders are retained in theirpre-determined position. The biasing of the piston towards the cam byhydraulic medium pressure provides the advantage of a certain elasticityof the piston in cam-remote direction so that indefinite switchingstates do not result in a destruction of components.

According to the invention, the locked position of the sliders isestablished trigger-like via a groove in the outer peripheral surface ofthe cam. However, other geometric shapes such as elevations and the likemay also be used in place of the groove to trigger the locking step.But, in this case, the switching mechanism would have to beappropriately modified.

In an advantageous embodiment of the invention, the piston is arrangedin the region of the bottom of the annular section. This has theadvantage over an arrangement in the circular section that the annularsection is in almost permanent contact with its cam and reliableswitching information can thus be transmitted to the sliders even in theswitched-off state of the tappet.

The subject matter of the invention also includes the arranging of acommon pressure chamber under a tappet-side end of the piston for asimultaneous pressure medium supply to the associated slider. Thispressure chamber is designed for a servo means such as hydraulic medium.Alternatively, a separate supply of hydraulic medium may be implementedfor the slider and the piston starting from the outer peripheral surfaceof the tappet. Insofar as the tappet also comprises a hydraulicclearance compensation mean, a three-way supply of hydraulic medium tothe tappet is also conceivable.

Due to the fact that the outer slider comprises a bore starting from itsradially outer end, a further radial enlargement of design space forcreating a pressure chamber in front of this slider can be dispensedwith.

According to a further proposition of the invention, a returndisplacement of the sliders in uncoupling direction is achieved by theforce of a compression spring. However, the invention likewise includessolutions in which the sliders are also displaced back into theiruncoupling position by a hydraulic medium or another servo means. It isfurther possible to configure the piston so that its cam-proximate edgeis made as a control edge. In this case, according to the invention, thecontrol edge comprises a reinforcement which may, for instance, take theform of needles or balls or the like. It is equally possible toreinforce only the edge region itself or to provide the edge region witha wear-resistant coating.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described more closely with the help of thedrawings in which:

FIG. 1 is a longitudinal section through a tappet comprising thefeatures of the invention, taken along the intersection line shown inFIG. 2;

FIG. 2 is a cross-section through a tappet according to FIG. 1 in theregion of its sliders;

FIGS. 3, 4 are longitudinal sections through the tappet of FIG. 1, takenalong the intersection line of FIG. 1 and showing the coupled and theuncoupled state respectively, of the piston;

FIG. 5 is a schematic representation of a grooved cam for loading theannular section; and

FIGS. 6-8 are enlarged representations of the piston showing specialconfigurations of the control edge.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a tappet of a kind known, per se, in the technical field.The tappet 1 comprises an outer annular section 2 having a bottom 3which is loaded by two high lift cams 4 in lifting direction. Theannular section 2 concentrically surrounds a circular section 5. Thiscircular section 5 is loaded in the region of its bottom 6 by a low orzero lift cam 7. It is also possible to reverse the cam arrangement, butthen, the outer annular section 2 would have to cooperate with a gasexchange valve, not shown. In the instant example, the circular section5 cooperates through a hydraulic clearance compensation element 8, notdescribed further, with at least one gas exchange valve of the internalcombustion engine.

Each of the sections 2, 5 possesses in the region of its bottom 3, 6, aradially extending reception, 9 and 10 respectively, and thesereceptions 9, 10 are aligned to each other in the base circle of thecams 4, 7 associated to the sections 2, 5. These receptions 9, 10 aremade in the present case as bores. A first, radially inwardsdisplaceable slider 11 is disposed in the first reception 9 of theannular section 2. This slider 11 has the geometry of a piston andextends in the uncoupled state of the sections 2, 5, with an inner endface 12 immediately in front of an annular surface 13 between thesections 2, 5. A second slider 14 is arranged radially inwards behindthe slider 11 in the reception 10 of the circular section 5, and saidsecond slider 14 extends preferably through the entire length of thereception 10 of the circular section 5 and is likewise configured as apiston.

Due to the position of the sliders 11, 14 in the state represented inFIG. 1, the tappet 1 follows only the lift of the cam 7 in this state.To switch the tappet 1 to the lift of the high lift cams 4, hydraulicmedium can be routed to the radially outer end face 15 of the firstslider 11. To optimize design space, the slider 11 comprises a bore 16starting from its outer end face 15. This bore 16 comprises a radialopening 17 into which hydraulic medium can be fed from a pressurechamber 18 situated in axial direction therebelow. Radially outwards,the reception 9 is delimited by a plug 19 on which the slider 11 can,but must not be supported through its end face 15. In the presentembodiment, the plug 19 is pot-shaped and serves at the same time as aslideway for the slider 11. The plug 19 and the slideway may also bemade as separate components, in which case, the slideway is configuredas a bushing.

When it is desired to establish a coupling of the two sections 2, 5 inthe base circle phase of the cams 4, 7, the slider 11 is displacedradially inwards by applied hydraulic medium pressure so that itsperipheral surface 20 overlaps the annular surface 13. At the same time,the slider 11 acts through its inner end face 12 on the second slider 14so that the peripheral surface 21 thereof overlaps the annular surface13 on the opposite side and extends partially in a further part of thereception 9 of the section 2. The reception 9 is bored preferably in asingle work step.

A return displacement of the sliders 11, 14 for uncoupling the sections2, 5 is achieved in the present embodiment by the force of a springmeans 22 in the form of a compression spring surrounding the secondslider 14. At the end of the spring means 22 nearer the first slider 11,at least one coil of the spring means 22 is retained in an annulargroove 23 of the second slider 14, the spring means 22 being supportedat the other end on a diameter reduction 24 of the reception 10. Thisdiameter reduction 24 can serve, at the same time, for example, as abushing and slideway for the second slider 14. Due to thisconfiguration, it is not necessary to arrange an additional slideropposite the first slider 11 in the annular section 2.

As a person skilled in the art can further see from FIGS. 1 to 4, thefirst slider 11 is partially surrounded by a recess 25 of a piston 26which is displaceable in the longitudinal direction of the tappet 1.This piston 26 extends in cam direction through an aperture 27 in thebottom 3 of the annular section 2.

A cam-remote portion of the recess 25 possesses an edge 28 configured asa control edge. At the same time, the associated cam 4 comprises atleast in the second part β of its base circle, a groove 29 extending inperipheral direction. In addition, the first slider 11 comprises twoaxially spaced annular grooves 30, 31 (see particularly FIG. 2). When,as described more closely in the introductory part of the specification,the sliders 11, 14 have to be held during the second part β of the cambase circle in the position shown in FIG. 1 for uncoupling, the piston26 is loaded in cam direction on its cam-remote end face 32 by thehydraulic medium pressure provided by the pressure chamber 18, so that apart of the control edge 28 of the piston 26 extends in the annulargroove 30. In this way, the sliders 11, 14 are prevented from beingaxially displaced, and switching errors are thus reliably excluded in arelatively simple manner.

For a coupling of the sections 2, 5, which is advantageously realized ina first part α of the base circle of the cam 4, the sliders 11, 14 arepushed radially from the left to the right as seen in FIG. 1. When thecoupling position is reached, and this is the normally the case during arotation of the cam, the piston 26, assisted by the hydraulic medium,engages into the groove 29 by its cam-proximate end 33 at the start ofthe groove 29 and extends at the same time with its control edge 28 inthe outer annular groove 31. In this case, too, indefinite movements ofthe sliders 11, 14 are prevented.

For a better understanding, FIG. 3 shows the piston 26 extending intothe groove 29 of the cam 4. The control edge 28 is engaged in one of theannular grooves 30 or 31.

In contrast, FIG. 4 shows the piston 26 in its uncoupled position. Thecontrol edge 28 has released the slider 11 which is thus freely movableduring the base circle phase α of the cam 4.

FIGS. 6 to 8 show special alternatives for configuring the control edge28 of the piston 26. For example, FIG. 6 shows that the control edge 28can be reinforced with a needle 35, or FIG. 8, that it can be providedwith a ball 36. It is understood that a variety of reinforcementelements, needing no further description here, will come to the mind ofa person skilled in the art. FIG. 7 shows further that the control edge28 can be made in one piece with the rest of the piston 26 and comprise,for example, a reinforcement 37 for reducing wear.

What is claimed is:
 1. A tappet (1) for a valve train of an internalcombustion engine, which tappet (1) can be switched to different valvelifts and is comprised of an outer annular section (2) whichconcentrically surrounds a circular section (5) which is axiallydisplaceable relative thereto, both sections (2,5) being loadable inlift direction in the regions of their bottoms (3,6) by cams ofdifferent lifts, or at least one section being loadable by at least onecam in the lift direction, each of the sections (2,5) comprising in theregion of its bottom (3,6) at least one reception (9,10) extendingradially, said receptions (9,10) being aligned to each other in a cambase circle phase, there being arranged in the reception (9) of theannular section (2) a first slider (11) which is displaceable by a servomeans towards the reception (10) of the circular section (5), and saidfirst slider (11), for realizing un uncoupling of the sections (2,5)extends with an inner end face (12) up to a position immediately infront of an annular surface (13) between the sections (2,5), and, forrealizing a coupling of the sections (2,5), acts on a second slider (14)which extends through an entire length of the reception (10) of thecircular section (5), so that both sliders (11,14) overlap the annularsurface (13) by their peripheral surfaces (20,21) to establish a coupledstate, characterized in thatone of the sliders (11 or 14) whose section(2 or 5) cooperates with a cam (4 or 7) is surrounded on its peripheralsurface (20 or 21) at least partially by a recess (25) of a piston (26)or a piston-like element, the piston (26) or the piston-like element isdisplaceable in an axial direction of the tapped (1) by a servo means,and the recess (25) comprises a cam-remote control edge (28) whichengages the slider (11 or 14), the piston (26) or the piston-likeelement extends through an aperture (27) of the bottom concerned (3 or6) and cooperates with a groove (29) extending in a peripheral directionon the outer peripheral surface (38) of the associated cam (4 or 7),said groove (29) starts on a second part (β) of the base circle, one ofthe sliders (11 or 14) comprises two annular grooves (30,31) into whichthe control edge (28) of the piston (26) or the piston-like element canbe selectively displaced when said piston (26) or piston-like element issimultaneously engaged in the groove (29) of the associated cam (4 or7), and the annular grooves (30,31) are spaced from each other so thatwhen the control edge (28) displaced into the radially inner annulargroove (30), the sliders (11, 14) extend entirely within theirrespective receptions (9,10) for uncoupling the sections (2,5) and whenthe control edge (28) is displaced into the radially outer annulargroove (31), the peripheral surfaces (20,21) of the sliders (11,14)overlap the annular surface (13) between the sections (2,5) for couplingthe sections (2,5).
 2. A tappet according to claim 1, characterized inthat the piston (26) or the piston-like element is arranged in theannular section (2).
 3. A tappet according to claim 2, characterized inthat the servo means for displacing the piston (26) or the piston-likeelement is a hydraulic medium.
 4. A tappet according o claim 3,characterized in that a pressure chamber (18) for the hydraulic mediumextends axially under a cam-remote end (32) of the piston (26), saidpressure chamber (18) being closed in cam-remote direction by a ring(39) which borders on the annular section (2).
 5. A tappet according toclaim 4, characterized in that a common supply of hydraulic mediumpressure to a radially outer end face (15) of the first slider (11) andto the piston (26) is provided from the pressure chamber (18).
 6. Adevice according to claim 5, characterized in that the radially outerend face (15) of the first slider (11) comprises a bore (16) and, in theuncoupled state, bears against a plug (19) which closes the reception(9) of the first slider (11) in radially outward direction, the bore(16) comprising at least one radial opening (17) which is in hydrauliccommunication with the pressure chamber (18).
 7. A tappet according toclaim 2, characterized in that the groove (29) of the cam (4) extends inthe second part β of its base circle and in the region of its run-onflank γ.
 8. A device according to claim 2, characterized in that therecess (25) of the piston (26) is made as a longitudinal groove whosecam-remote edge (28) forms the control edge and extends at any desiredinclination.
 9. A tappet according to claim 8, characterized in that theedge (28) possesses a reinforcement (35, 36, 37) at least in a contactregion.
 10. A tappet according to claim 9, characterized in that theedge (28) comprises a separate component including at leas tone of aneedle (35) or a ball (36) in the contact region.
 11. A tappet accordingto claim 2, characterized in that the sliders (11, 14) are displaceablein uncoupling direction by a mechanical spring means (22).
 12. A tappetaccording to claim 11, characterized in that the spring means (22) is atleast one compression spring which surrounds the second slider (14) andis fixed at an end nearer the first slider (11) on the second slider(14) or in an annular groove (23) of the second slider (14) while beingsupported at another end on a diameter reduction of the reception (10)of the second slider (14).